UNITED NATIONS (CNN) - President Barack Obama's ambassador to the United Nations, Susan Rice, arrived for her first day on the job Monday calling the U.N. a "great institution" but saying there is "room for improvement."

Rice presented her credentials to U.N. Secretary-General Ban Ki-moon at U.N. headquarters in New York Monday morning. She said the two then spoke for 45 minutes, discussing a wide range of international issues, including the situations in Sudan and the Middle East.

After meeting with Ban, Rice spoke to reporters in front of the U.N. Security Council chambers, laying out several key issues that the Obama administration hopes to accomplish at the United Nations: Strengthening the capacity to engage in complex peace operations, advancing U.S. and "collective" interest on climate change and nuclear proliferation, and putting the United States at the center of poverty reduction and fighting disease, cornerstones of the U.N. Millennium Development Goals.